Such a statistical measurement equipment is already known from the Belgian patent application No. 08701481 (W. VERBIEST 3) and the international patent application No. PCT/EP88/00594 (P. JOOS 1). It forms part of a telecommunication switching system operating according to the Asynchronous Transfer Mode (ATM), i.e. wherein data are transmitted under the form of cells or packets of bits and with a variable cell rate. An individual cell stream is allowed to be multiplexed on a same telecommunication link together with a plurality of other individual cell streams already multiplexed thereon, if an allocation formula is satisfied. This formula is based on the expected values of the mean and variance of the probability distribution function of the cell rate of the individual cell stream, on the expected values of the mean and variance of the probability distribution function of the cell rate of each of the above mentioned other individual cell streams already multiplexed on the link, as well as on the maximum allowable bandwidth on this link. This allocation formula is based on the assumption that a multiplex of a relatively high number of uncorrelated probability distribution functions leads to the normal probability distribution function, as follows from the Central Limit Theorem. However, because the mean and variance do not sufficiently define an arbitrary probability distribution function of the cell rate of a cell stream and if the number of cell streams of a multiplex is relatively low, e.g. 10, the resultant probability distribution function may be far from a normal one. As a consequence the use of the above allocation formula may give rise to an overload of the communication link.
As also described in the above literature the known statistical measurement equipment is able to measure the values of the mean and variance of the cell rate of each individual cell stream of a multiplex. The purpose of this measurement is to check if the source of this individual cell stream operates within the limits on the basis of which its multiplexing on the link was allowed. To this end the measurement equipment more particularly determines the value of the mean and variance of the cell rate of each individual cell stream at the receipt of each cell of this individual cell stream and compares the thus measured values with the above mentioned respective expected values thereof. Depending on the result of this comparison the received cell is then either allowed for further processing or discarded. But because the probability distribution function of the cell rate of the multiplex is not a normal one it may happen that the equipment erroneously allows a cell to be processed further.
From the above it follows that errors may occur because the probability distribution function of the cell rate of each cell stream is not always sufficiently defined by its mean and variance. More particularly, it has been found that errors are especially due to the fact that the tail of the probability distribution function of the cell rate is not sufficiently defined by these two parameters.